Identification of air and/or fuel metering drift

ABSTRACT

The disclosure relates to a system and method for identifying whether a difference between measured lambda and computed lambda, based on mass air flow and mass fuel flow, is due to a drift in fuel metering or a drift in air metering. The determination is based on also measuring exhaust gas NOx using a NOx sensor. By comparing the measured NOx to modeled NOx, drift can be attributed appropriately to the air flow measurement and/or the fuel flow measurement. Appropriate correction in the calibration can be undertaken to overcome sensor drift and/or drift in the fuel injector/fuel system flow characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to DE 10 2009 029 257.8, filed Sep. 8, 2009, which is herebyincorporated by reference it its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a method for identifying and correcting driftof fuel and/or air quantity metering in an internal combustion engine.

2. Background Art

Measuring an exhaust-gas lambda value is one possibility for identifyinga drift in the fuel metering or in the air quantity metering. This maybe achieved by virtue of an estimated lambda value being calculated onthe basis of a measured mass air flow and the original set value of thefuel quantity. The measured mass air flow may be determined by an massair flow sensor, a so-called MAF sensor.

The drift of the MAF sensor with progressive service life may amount toup to +/−5%. The drift of the fuel injection quantity with progressiveservice life may amount to up to +/−15%. In background systems, it isnot possible to determine whether the drift is to be attributedprimarily to the parameter “air” or to the path of the MAF sensor or tothe parameter “injected fuel” for example on account of a blockedinjector or injector system or on account of wear of the injector or ofthe injector system.

The invention is therefore based on the object of providing a method ofthe type specified in the introduction, by means of which it is possibleto determine which parameter the deviation is to be attributed to, inorder to be able to reset said parameter in a targeted fashion.

SUMMARY

To overcome at least one problem, a lambda sensor and a NOx sensor areused to allow detection of whether drift is occurring in fuel meteringand/or air metering. In one embodiment, a first NOx value is estimatedbased at least on a measured mass air flow, a measured lambda, and anamount of burned gas in the intake gas. NOx is also measured. A firstdelta NOx based on a difference between the first NOx value and themeasured NOx is determined. A first delta NOx value is compared to afirst threshold and a drift in a mass fuel flow measurement is inferredwhen the first delta value is less than the first threshold. If such adrift in mass fuel flow, calibration coefficients associated with themass fuel flow measured are corrected. In some embodiments, the firstNOx value is further based on engine operating conditions. In someembodiments, the first delta NOx is based on the difference between thefirst NOx value and the measured NOx squared integrated over apredetermined period of time.

A second NOx value is based at least on a measured mass fuel flow, themeasured lambda, and the amount of burned gas in the intake gas, asecond delta NOx based on a difference between the second NOx value andthe measured NOx is determined. A second delta NOx value is compared toa second threshold; and a drift in a mass air flow measurement isinferred when the second delta value is less than a second threshold.Calibration coefficients associated with the mass air flow measurementare corrected when the drift in mass fuel flow is inferred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an internal combustion engine; and

FIG. 2 is a process diagram of the procedure according to an embodimentof the disclosure.

DETAILED DESCRIPTION

As those of ordinary skill in the art will understand, various featuresof the embodiments illustrated and described with reference to any oneof the Figures may be combined with features illustrated in one or moreother Figures to produce alternative embodiments that are not explicitlyillustrated or described. The combinations of features illustratedprovide representative embodiments for typical applications. However,various combinations and modifications of the features consistent withthe teachings of the present disclosure may be desired for particularapplications or implementations.

FIG. 1 shows an engine 100 having an intake 102 with a mass air flow(MAF) sensor 104 disposed in intake 102. Alternatively, mass air flowcan be determined by other combinations of sensors, such as candetermine engine speed and intake density. Engine 100 has an exhaust 106with a sensor 108 or sensors. Sensor 108 may be an exhaust oxygen sensor(lambda sensor) based on which stoichiometry in the exhaust can bedetermined. Stoichiometry can be expressed as an air-fuel ratio,equivalence ratio, lambda, as examples. Herein, lambda is used. In someembodiments, sensor 108 is a combine NOx/O2 sensor. Alternatively,individual sensors for NOx and O2 are provided. Fuel tank 110 is coupledto a fuel pump 112 (alternatively, multiple fuel pumps) to provide fuelinjectors 114. An electronic control unit (ECU) 120 is coupled to thesensors 104, 108, and other engine sensors 116, such as engine speed,fuel injection pressure, intake temperature, exhaust gas recirculationparameters, as examples. Also, ECU 120 commands injection events to fuelinjectors: number of events, timing of events, and duration of events.FIG. 2 shows a process diagram 1 for identifying and correcting a driftin a fuel and/or air quantity metering from commanded quantities ininternal combustion engines. Within the context of this disclosure,drift is a slow change of a value from a predefined magnitude over time.

Based on a lambda sensor, it can be determined if there is a drift inthe air metering or the fuel metering. But, based on a single sensor, itcannot be determined which is causing the drift. According to anembodiment of the disclosure, the NOx sensor reading is used as a secondmeasure of drift. By using both sensor signals, a drift can beattributed to either the fuel or air metering and an appropriatecorrection can be applied.

Referring to FIG. 2, process 1 begins in a start block 2. In block 3, anestimated fuel mass flow is determined based on lambda and a mass airflow as determined based on the mass air flow (MAF) sensor. The lambdaand MAF measurements are assumed accurate and the fuel flow isdetermined from those measurements. In block 4, a first NOx value isdetermined based on a NOx model using estimated fuel mass flow (fromblock 3), measured lambda, MAF, burned mass proportion in the intakegas, and the operating state of the internal combustion engine.

In block 5, a first delta NO_(x) (ΔNO_(x, 1)) for the first NOx value isdetermined. For this purpose, a difference between the measured NO_(x)value and the previously estimated first NO_(x) value (block 4) isdetermined. The difference between the two values is squared andintegrated over a predefined time window of for example 300 seconds.

In a decision block 6, it is determined whether the first delta NO_(x)for the first NOx value is smaller than a first threshold value. If thisis the case, control passes to block 7 in which drift of the injector orof the fuel injection system is inferred so that a correction to theinjector or the injection system calibration is applied. Control passesthen to block 8 where the process ends.

Within the context of the disclosure, the first threshold value is ameasured magnitude which is determined during a calibration of theinternal combustion engine during test runs for nominal emission levels.

If it is detected in decision block 6 that the first delta NO_(x) isgreater than or equal to a first threshold, control passes to block 9.

In block 9, a mass air flow is estimated based on measured lambda andthe injected fuel quantity. That is, accuracy in lambda and the injectedfuel quantity is assumed and an estimated mass air flow is determinedbased on those.

Subsequently, in a block 10, a second estimate of NOx emissions is basedon fuel mass flow, the estimated MAF signal, lambda, estimation ofburned mass proportions in the intake gas, and operating states of theinternal combustion engine.

In a block 11, a second delta NO_(x) (ΔNO_(x, 2)) for the second extremeis determined. For this purpose, a difference between the measuredNO_(x) and the previously (block 10) second estimated NO_(x) isdetermined. The difference is integrated over a predefined time windowof for example 300 seconds.

In a decision block 12, it is detected whether the second delta NO_(x)is smaller than a second threshold. If this is the case, control passesto block 13 in which drift of the MAF sensor is inferred appropriatecorrection of the MAF sensor is carried out. The method then ends in ablock 14.

If, in decision block 12, it is detected that the second delta NO_(x) isgreater than or equal to the second threshold, control passes to block15 and no adaptation or correction is applied. Control then ends inblock 16. Process 1 can be repeated periodically.

With the method according to the disclosure, it is possible to determinewhether a drift in air metering or a drift in fuel metering is causing adrift between lambda as measured and lambda as determined based on MAFand commanded mass fuel flow. For this purpose, a lambda sensor and anexhaust-gas NO_(x) sensor are used. In one embodiment, the two sensorsmay also be combined in one component. The proposed solution is based ona direct measurement not only on lambda in the exhaust gas, but also onNO_(x) concentration.

While the best mode has been described in detail, those familiar withthe art will recognize various alternative designs and embodimentswithin the scope of the following claims. Where one or more embodimentshave been described as providing advantages or being preferred overother embodiments and/or over background art in regard to one or moredesired characteristics, one of ordinary skill in the art will recognizethat compromises may be made among various features to achieve desiredsystem attributes, which may depend on the specific application orimplementation. These attributes include, but are not limited to: cost,strength, durability, life cycle cost, marketability, appearance,packaging, size, serviceability, weight, manufacturability, ease ofassembly, etc. For example, it may be desirable to have an extensive setof sensors to provide an accurate assessment of the state of vehicleaccessories. However, to maintain a desirable cost structure, asatisfactory estimation of some accessory quantities may be ascertainedby inferring from a lesser set of sensor data. The embodiments describedas being less desirable relative to other embodiments with respect toone or more characteristics are not outside the scope of the disclosureas claimed.

What is claimed:
 1. A method for identifying drift in at least one offuel metering and air metering in an internal combustion engine,comprising: estimating a first NOx value based at least on a measuredmass air flow, a measured lambda, and an amount of burned gas in theintake gas; measuring NOx; and determining a first delta NOx based on adifference between the first NOx value and the measured NOx.
 2. Themethod of claim 1, further comprising: comparing a first delta NOx valueto a first threshold; and inferring a drift in a mass fuel flowmeasurement when the first delta value is less than the first threshold.3. The method of claim 2, further comprising: correcting calibrationcoefficients associated with the mass fuel flow measurement when thedrift in mass fuel flow is inferred.
 4. The method of claim 1 whereinthe first NOx value is further based on engine operating conditions. 5.The method of claim 1, further comprising: estimating a fuel mass flowbased on the measured mass air flow and the measured lambda wherein thefirst NOx value is further based on the estimated fuel mass flow.
 6. Themethod of claim 1 wherein the first delta NOx is based on the differencebetween the first NOx value and the measured NOx squared with thesquared difference integrated over a predetermined period of time. 7.The method of claim 1, further comprising: comparing a first delta NOxvalue to a first threshold; estimating a second NOx value based at leaston a measured mass fuel flow, the measured lambda, and the amount ofburned gas in the intake gas when the first delta value is greater thanthe first threshold; determining a second delta NOx based on adifference between the second NOx value and the measured NOx; comparingthe second delta NOx value to a second threshold; and inferring a driftin a mass air flow measurement when the second delta value is less thana second threshold.
 8. The method of claim 7, further comprising:correcting calibration coefficients associated with the mass air flowmeasurement when the drift in mass fuel flow is inferred.
 9. A systemfor identifying drift in at least on of fuel metering and air meteringin an internal combustion engine, comprising: fuel injectors coupled toengine cylinders; a mass air flow (MAF) sensor disposed in an engineintake; a lambda sensor disposed in an engine exhaust; a NOx sensordisposed in the engine exhaust; and an electronic control unitelectronically coupled to the fuel injectors, and the MAF, lambda, andNOx sensors wherein the electronic control unit uses signals from thelambda sensor and the NOx sensor to determine whether mass fuel flowbased on commands to the fuel injector has drifted and whether measuremass air flow based on the MAF sensor has drifted.
 10. The system ofclaim 9 wherein the electronic control unit estimates a first NOx valuebased at least on signal from the lambda sensor, the MAF sensor and anestimated amount of burned gas in the intake gas; the electronic controlunit determines a measured NOx from a signal from the NOx sensor; andthe electronic control unit determines a first delta NOx based on asquare of a difference between the first NOx value and the measured NOxintegrated over a predetermined period of time.
 11. The system of claim10 wherein the electronic control unit further compares the first deltaNOx value to a first threshold and the drift in the measured mass fuelflow is determined when the first delta value is less than the firstthreshold.
 12. The system of claim 10 wherein the electronic controlunit further: compares the first delta NOx value to a first threshold:determines no drift when the first delta NOx is greater than the firstthreshold; estimates a second NOx value based at least on signal fromthe lambda sensor, commands to the fuel injectors and an estimatedamount of burned gas in the intake gas; and the electronic control unitdetermines a second delta NOx based on a square of a difference betweenthe second NOx value and the measured NOx integrated over apredetermined period of time.
 13. The system of claim 12 wherein theelectronic control unit further compares the second delta NOx value to asecond threshold and the drift in the measured mass air flow isdetermined when the second delta value is less than the first threshold.14. The system of claim 9 wherein the lambda sensor and the NOx sensorare integrated into a single sensor.
 15. The system of claim 9 whereinthe measured mass fuel flow is based at least on energizing timecommanded to the fuel injectors and a pressure in fuel lines coupled tothe fuel injector.
 16. A method for identifying drift in at least one offuel metering and air metering in an internal combustion engine,comprising: estimating a mass fuel flow based on a measured mass airflow and a measured lambda; estimating a first NOx value based at leaston the estimated mass fuel flow, the measured mass air flow, themeasured lambda, and an amount of burned gas in the intake gas;measuring NOx; and determining a drift in fuel metering based on adifference between the first NOx value and the measured NOx.
 17. Themethod of claim 16, further comprising: estimating a mass air flow basedon a measured mass fuel flow and the measured lambda; estimating asecond NOx value based at least on the estimated mass air flow, themeasured mass fuel flow, the measured lambda, and the amount of burnedgas in the intake gas; and determining a drift in air metering based ona difference between the second NOx value and the measured NOx.
 18. Themethod of claim 17, further comprising: correcting drift in fuelmetering when the square of the difference between the first NOx valueand the measured NO integrated over a predetermined period of time isless than a first threshold; and correcting drift in fuel metering whenthe square of the difference between the second NOx value and themeasured NO integrated over a predetermined period of time is less thana second threshold.
 19. The method of claim 16 wherein the measured massfuel flow is based at least on commands to fuel injectors coupled toengine cylinders and pressure of fuel supplied to the fuel injectors.20. The method of claim 16 wherein the measured mass air flow is basedon a signal from a mass air flow sensor.